One of the problems in understanding human biological processes is the inability to study the processes in humans. For the most part, studies have had to be made on animals or mammals and the information obtained extrapolated to humans. In many situations, the animals used as surrogates are adequate to varying degrees.
Recently, the introduction of human fetal tissue into scid/scid mice has been reported, where thymus, lymph node and fetal liver have been introduced into the mouse to provide for various aspects of a human immune system in the mouse. These chimeric mice have found use in studying of HIV infection and the ability of drugs to counteract the infection. The chimeric animals therefore offer potential new opportunities for investigating various processes associated with human physiology and pathology.